God commanded Moses to deliver the following message to the Israelites:
"Therefore, tell the people that I am God.
I will take you away (והוצאתי) from your forced labor...
and I will free you (והצלתי) from their slavery...
I will liberate you (וגאלתי)...
and I will take you (ולקחתי) to Myself as a nation." (Exodus 6:6-7)
The Midrash notes that the word "Therefore" (לכן) is the language of an oath. God had promised to redeem the Jewish people from Egyptian slavery.
Why was this oath necessary? And why did God say that He would save the Jewish people using "Four leshonot (expressions) of Redemption"?
The Wise Doctor
There was once a man with a serious disease, one that caused many health issues. His illness gave him headaches; he had trouble sleeping, he lacked a good appetite, and his bones would often hurt.
The sick man went to a highly regarded physician, in the hope that the doctor would be able to heal him quickly.
Upon examining the patient, however, Dr. Weinberg realized that it would be impossible to immediately heal him. It would take time to cure him from such a serious illness. However, the doctor did not want to discourage the patient. A wise man, he recognized the importance of a cheerful and optimistic outlook to the healing process.
Therefore, Dr. Weinberg told the sick man: "Do not worry, my friend. I will heal you step by step. First I will cure your headaches, then I will restore your sleeping patterns, then I will help you recover your appetite, and then I will ease the aching pains in your bones."
Still, the doctor realized that these words might discourage his patient. The poor man might think that he was unable to truly cure him, and could only alleviate some of the side effects of his illness.
Therefore, at the very start, Dr. Weinberg turned to the patient and said, "I promise you that in time you will be completely cured. And now I will start by helping you with these various ailments."
God announced that He would redeem Israel, using four leshonot or phrases. Why four phrases? This indicated that the Exodus from Egypt would not be a complete redemption of the Jewish people. Rather, it was a partial redemption, rescuing them from their many immediate problems.
But God did not want the Jewish people to loose faith. So He first promised, "Lachein, tell the people that I am God." This, as the Midrash explains, is the language of an oath. God promised that now He would help the Jewish people, rescuing them from the hardships and slavery of Egypt. But in the future, He would fully redeem them, with a complete and permanent redemption.
(Adapted from Mishlei Yaakov, pp. 119-121)